Many previously known high temperature polymer resins, including polyimides and polyamide-imides, suffer from their inability to be processed at elevated temperatures. These resins are often characterized by their insolubility and infusibility properties which make them practically impossible to process with conventional plastics processing equipment.
In the case of polyimide and polyamide-imide resins, the resins are usually handled in the form of their precursor polyamide acids. But even here, the precursor materials, while suitable for the preparation of thin films prepared from solution, cannot be handled by autoclaving and press molding techniques without great difficulty. The polyamide acid forms of both the polyimide and polyamide-imide resins undergo cyclization to the imide form during processing, giving rise to poorly consolidated and void filled parts of low mechanical strength.
It has now been found that, through the use of prepolymers end capped with azadiene groups or mixtures of such azadiene prepolymers with low melting compounds containing reactive carbon-carbon double bonds, i.e., dienophiles, it is possible to process these materials using conventional plastic processing techniques, such as autoclave and vacuum bag laminating, compression and injection molding. The mixtures of azadiene prepolymers and dienophiles were unexpectedly found to be processable and curable at much lower temperatures than previously reported high temperature prepolymers to yield high strength thermoset resins with negligible void contents. Suitable dienophiles contain one, two or more reactive carbon-carbon double bonds, preferably two double bonds.